1. Field
The embodiments discussed herein are directed to a recording medium having recorded therein a communication program for transferring information, a relay node and a communication method.
2. Description of the Related Art
In recent years, mechanically controlled apparatuses such as automobiles, industrial robots and humanoid robots have been modularized according to function. With sensors having a network function, the terminal devices (modules) mounted on the mechanically controlled apparatus may make up a network.
In these mechanically controlled apparatuses including a network, real time communication and non-real time communication may coexist. The real time communication may be conducted periodically for feedback control, for example, and has a small absolute delay, while the non-real time communication is the communication which, though not required to have the real time property, may be required to have a high throughput such as the distribution of a correction program or the file transfer.
On the other hand, the mechanically controlled apparatus including a network desirably uses a multipurpose network (for example, Ethernet) including a centralized distribution device such as a switching device in the path to secure the flexibility and extendibility and the ease with which a system configuration is implemented.
In a case where a plurality of inputs transferred to the same output terminal of the switching device exceed the throughput of the output terminal, however, the communication queue in the switching device would generally grow. The network including a switching device midway of the path, therefore, poses the problem that the growth of the communication queue often increases the communication delay and causes the loss of packets, thereby making it difficult to carry out the real time communication properly.
In view of this, a conventional technique is available in which the periods of carrying out the real time communication and the non-real time communication are differentiated temporally taking advantage of the periodicity of the real time communication. Teethe terminal device at the receiving end monitors the communication situation of the data transmitted thereto to detect the non-real time communication interfering with the real time communication, and by limiting the flow rate of the non-real time communication, prevents the growth of the communication queue in the switching device (see, for example, Japanese Unexamined Patent Publication No. 10-107769).
The conventional technique described above, however, fails to take into consideration the topology in which the terminal devices for transmitting and receiving the data are connected through a plurality of switching devices. The network including a plurality of switching devices on the path connecting the terminal devices, therefore, harbors the problem that it is difficult to control the flow rate of the non-real time communication, so that the real time communication may not be carried out properly.
Another problem is that as long as a network system cannot be constructed using a plurality of switching devices, the maximum number of connectable terminal devices is limited, thereby reducing the flexibility and extendibility of the system configuration.
FIG. 22 illustrates problems of a conventional technique. In a network system 2200, terminal devices 2201 to 2203 and terminal devices 2204 to 2206 are connected to each other through switching devices 2210, 2220. Terminal devices 2201 to 2203 are defined as the transmitting end, and the terminal devices 2204 to 2206 as the receiving end.
In the network system 2200, the data transmitted from the transmitting end to the receiving end conflict with each other between the switching device 2210 and the switching device 2220. In the process, the data transmitted from the terminal devices 2201, 2202 to the terminal device 2204 can be detected by the terminal device 2204.
The data transmitted from the terminal device 2203 to the terminal device 2206, however, cannot be detected by the terminal device 2204. At the receiving end, therefore, it is difficult to control the flow rate correctly by detecting the non-real time communication interfering with the real time communication. The communication queue is increased in the switching device 2210 and the data for the real time communication may not be processed within a specified time.